It is anticipated that mobile traffic will increase drastically in the coming years, and some estimate that mobile traffic will increase more than 500 fold in the coming decade. In order to cater for this massive increase in mobile traffic, new solutions that increase the capacity of mobile networks are required.
An important aspect of increasing system capacity in cellular communication has been the design of cost-effective radio access technologies (RATs). Typically, RATs are characterised by multiple access schemes, such as frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA) and orthogonal-frequency division multiple access (OFDMA), each of which provides means for multiple users to access and share the system resources simultaneously.
Current mobile communication systems such as 3GPP Long-Term Evolution (LTE) and LTE-advanced employ OFDMA for downlink (DL) and single carrier (SC)-FDMA for Uplink (UL). The use of OFDMA in LTE enables relatively good system capacity, while retaining a relatively simple receiver design. Technically, a more advanced receiver design would enable a higher transmission rate, and thus improved bit rate per channel (i.e. time-frequency unit), boosting spectrum efficiency or spectrum utilisation.
It has been established that superposition coding transmission, together with advanced interference cancellation, can be used to achieve capacity on a Gaussian broadcast channel. Superposition coding is a non-orthogonal scheme which allows multiple users with considerably different Signal to Interference and Noise ratios (SINRs) to share the same resources (i.e. time and frequency resources such as LTE's REs) without the need of spatial separation. Due to its capacity achieving nature, superposition coding mechanisms have been identified as a candidate RAT for new air interfaces in 3GPP 5G networks, and have been endorsed for feasibility studies in 3GPP RAN. In principal, superposition coding or multiuser superposition transmission (MUST) may optimally exploit the channel ordering or the path loss difference of paired users served by the same transmission point.
As illustrated in FIG. 1, a UE 1 that is geographically closer to a base station has a higher channel gain or higher SINR than a UE 2 that is geographically further away from the base station. As such, a downlink transmission that can be decoded at the far UE (UE 2) can possibly be decoded at the near UE (UE 1), but not vice versa. Conceptually, the DL transmission power to the far UE is considerably higher than the DL transmission power to the near UE, to account for higher path loss.
MUST takes advantage of this considerable transmission power difference by superimposing the downlink transmissions for the near UE (with low transmit power) in to that for the far UE (with high transmit power) and transmitting the superimposed or composited signal in the same set of channel resources achieving multiple access gain in the power domain.
Due to the transmission power difference, the signal of the near UE (UE-1) hardly reaches the far UE (UE-2) and desirably appears as noise at the far UE (UE-2). This allows the far UE (UE 2) to decode its signal in the traditional way. Since near UE (UE-1) has a high channel gain, it can receive and decode far UE's signal, and cancel or remove the far UE's signal from the received signal to decode its own signal. This procedure at the near UE is called successive decoding or successive interference cancellation (SIC).
As discussed in further detail below, there are, however, challenges in employing MUST in various scenarios, including in a homogeneous network deployment, a heterogeneous network with non-co-channel deployment, and a heterogeneous network with co-channel deployment.
FIG. 2 illustrates a homogeneous network 10, according to the prior art. The network 10 includes a base station transmitter 11, having 2, 4, or 8 transmit antennas concurrently providing wireless connectivity services to a far UE 12 on a based signal 13 and to a near UE 16 on an extended signal 17 that is superimposed on the based signal 13 on the same channel resources. The far UE 12 may subject to measurable inter-cell interference 14 from neighbouring cells 15 operating on the same carrier frequency. Practically, the far UE 12 may be further subject to interference 18 caused by the extended signal 17 intended to the near UE 16, which does not perfectly decay to noise when it reach the far UE 12.
FIG. 3 illustrates a heterogeneous network 20, according to the prior art. The network 20 includes a base station transmitter 21, having 2, 4, or 8 transmit antennas providing mobility management to a plurality of UEs within its coverage, including UEs 23 and 26, on a first carrier frequency. The network 20 includes small cell base station transmitters, such as base station transmitter 22, within the coverage of macro base station 21, each of which may have two transmit antennas providing wireless connectivity services on a second carrier frequency to the far UE 23 on a based signal 24 and to the near UE 26 on an extended signal 27 that is superimposed on the based signal 24.
The far UE 23 may be subject to measurable inter-cell interference 25 from neighbouring small cell(s) operating on the same second carrier frequency. The near UE 26 may also be subject to measurable inter-cell interference 28 from other neighbouring small cell(s) operating on the same second carrier frequency. The far UE 23 may be further subject to and unaware of strong interference 29 caused by the extended signal 27 intended for the near UE 26, which does not perfectly decay to noise when it reach the far UE 23.
FIG. 4 illustrates a heterogeneous network 30 with co-channel deployment, according to the prior art. The network 30 includes a macro base station transmitter 31, having 2, 4, or 8 transmit antennas providing mobility management to a plurality of UEs with its coverage, and wireless connectivity services to some UEs including a far UE 32 on a based signal 33 and a near UE 36 on an extended signal 37 that is superimposed on the based signal 33. Other small cell base stations transmitters within the coverage of the macro base station 21 may have 2 transmit antennas providing wireless connectivity services on the same first carrier frequency to other UEs within their coverage.
The far UE 32 may be subject to measurable inter-cell interference 35 from neighbouring macro cell(s) and measurable intra-cell interference 34 from the small cells operating on the same carrier frequency. The near UE 36 may also subject to measurable intra-cell interference 38 from the small cell(s) operating on the same carrier frequency. The far UE 32 may further subject to and unaware of interference 39 caused by the extended signal 37 intended to the near UE 36 which does not perfectly decay to noise when it reach the far UE 32.
As such, there is a need to improve overall system performance in at least the above scenarios, therefore a need for an improved method and system for data communication in an advanced wireless network.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.